I'm from the school that will plant inground over a container any day. Is there a possibility that new owner might be able to grow inground? If yes, I would pot it and tell her to put inground ASAP. Frankly I don't see potted azaleas in my area. I don't see where you live and perhaps in your area potting azaleas is a common practice.

Yes, now is a good time to plant in your location. You do not need to break the root ball, just carefully extract them and plant them. Then water them, mulch them up to the drip line and you are set to go. Winter protection will help in case winter is unusually cold. I usually prepare for such spells by keeping my supplies handy but do not winter protect until the weather service says something. That got me in trouble this year though (NWS issued cold alerts and I slept thru them) and I ended with little bloom production from my mopheads. :o( They probably have those round fert pellets so do not fertilizer until next year. If you soi is alkaline, plan to amend the soil in Spring with garden sulfur, aluminum sulfate, greensand or iron-chelated liquid compounds. You can fertilize them with 1/2 to 1 cup of organic compost, composted manure, cottonseed meal or use a slow-release, general purpose chemical fertilizer per label directions. The location should provide the shrubs with afternoon/evening shade in the summer months. In their first few summers, count on seeing some wilting episodes since the shrubs like to pout in Years 1-3. If the soil is dry when they wilt, water them immediately. But if the soil is moist, they will recover on their own at night. When you water, water only the soil early in the mornings and aim to get moisture down to around 8-ish inches. I decide to turn on the drip irrigation when a finger inserted to a depth of 4" feels dry or almost dry.

It's not a concern I worry about :-) The chances are very slight. Potting soils are also referred to as 'soil-less mixes' - they contain no actual "dirt" :-) And the reason for that is not because it could harbor pathogens or insects (which can also become present in any potting soil mix as well) but because the texture and particle size of actual soil is not at all suited to the requirements of container culture. Garden/inground/top soils tend to be too fine a texture and too small a particle size to provide the porosity, proper aeration and fast drainage containers require. It is not so much a case of contamination as it is unsuitability. There are interface issues when you leave a rootball grown in garden soil intact when you pot into a container - two different soil structures in close proximity alter water movement and and drainage. But you get the exact same thing when planting from a nursery potted plant into the ground. Ideally, this is something you want to avoid. But it doesn't necessarily require total elimination. It is up to the gardener how thorough or precise they want to be in this effort and how well they know their plants and gardening skills. IMO, it is not a critical aspect of container culture.....others may have a different opinion.

I do it all the time. If a rose is struggling in the garden and needs some emergency TLC, I’ll dig it up, pot it, and coddle it until it is bigger and I’ve figured out what was wrong with that spot, even in the middle of the season.